The paper introduces parameter testing of the excitation system for No. 1 unit in Gansu Hanpingzui Hydropower Station. According to the field test data, the excitation system model for stability calculation is set up and the model parameters are obtained. No loading 5% step response of No.1 unit is simulated by BPA simulation software. The simulated result indicates the mathematical model and the parameters meet the actual situation and the needs of stability.